The call by Brown came after the Conservatives attacked Labour for its financial ties with the unions, the Guardian reported.

Eric Pickles, the Conservative Party chairman, wrote to the Prime Minister calling on him to condemn the cabin crew’s strike and suspend Labour’s financial relationship with Unite until the dispute has been resolved.

But a Downing Street source said the Prime Minister had already condemned the strikes.

The transport secretary, Lord Andrew Adonis, has also criticised the strikes as being “totally unjustified”.

Adonis told the BBC: “Let’s be absolutely clear the stakes are incredibly high in this strike and I absolutely deplore the strike.

“It is not only the damage it’s going to do to passengers and the inconvenience it’s going to cause – which is quite disproportionate to the issues at stake – but also the threat it poses to the future of one of our great companies in this country.

“It’s totally unjustified, this strike, on the merits of the issues at stake, and I do call on the union to engage constructively with the company.”

But Unite said Adonis “appears badly informed”. A spokesman for the union called on Adonis to pressure BA into reinstating its offer, which was retracted by the airline last week when Unite announced the strike dates.

BA’s offer included commitments on working hours and annual pay rises in exchange for the cabin crew workers agreeing to the BA’s planned £62.5m of cost cuts.

Unite had already made an offer to BA worth £63m, through a combination of pay-cuts and part-time working.

The Unite spokesman added: “If Lord Adonis is not prepared to speak out, he risks being seen as taking the part of a bullying and intransigent management.”